1. Field of the Invention
The present invention relates to a communication network system which has a high-ranking network employing a first communication protocol and a plurality of low-ranking networks employing a second communication protocol different from the first communication protocol, connected with one another through the high-ranking network, an interchange terminal connecting one of the low-ranking networks and the high-ranking network for each low-ranking network, a microcomputer of each interchange terminal which connects a transmission line of the low-ranking network with a transmission line of the high-ranking network without placing a microcomputer body between lines or separates the lines from each other, and a communication transmitter-receiver of each interchange terminal which is connected with the transmission line of the low-ranking network and the transmission line of the high-ranking network.
2. Description of Related Art
A communication protocol employed for a controller area network (CAN) or a local interconnect network (LIN) has been used for an on-board communication network system of a vehicle. Further, because high transmission speed and high reliability are important in the communication network system, FlexRay registered as a trademark has been recently used as a communication protocol for the communication network system.
Moreover, different communication protocols have been mixedly used in a single communication network system of a vehicle. In this case, as disclosed in the patent document of Published Japanese Patent First Publication No. 2009-027358, a gateway is used to connect communication networks, employing different communication protocols, with each other, and the protocol conversion is performed in the gateway.
Furthermore, as disclosed in the patent document of Published Japanese Patent First Publication No. 2005-328119, resources such as electronic control units (ECUs) and control programs designed for CAN have been effectively used for a communication network employing the FlexRay. More specifically, each of the ECUs is designed so as to have the same function as the function (i.e., protocol conversion) of the gateway, and these ECUs designed for CAN are used for a communication network employing the FlexRay.
In a network system based on these patent documents, a plurality of CANs employing a CAN protocol are, for example, connected with one another through a FlexRay communication network employing the FlexRay, and ECUs are used for each CAN. These ECUs are operated in response to data (hereinafter, called CAN protocol data) prepared based on the CAN protocol. In this case, even when CAN protocol data is transmitted between CANs through the FlexRay communication network to use the data only in the ECUs of the CANs, the protocol conversion is performed for the data in the FlexRay communication network.
Therefore, when error or problem in data communication from a first CAN to a second CAN occurs in the second CAN, the analysis of only signals transmitted in the second CAN is insufficient to investigate the cause of the error or problem. For this investigation, it is also required to analyze signals transmitted in the FlexRay communication network and to inspect software programs of the gateway executing the protocol conversion for the CAN protocol data. As a result, many inspection devices are needed, and it takes a long time to investigate error or problem occurring in the transmission of CAN protocol data through the FlexRay communication network.